By not having the wide aperture, it must make designing the lens easier and less complicated. From the size of it, it can't have much glass, so sharpness is easier to achieve. Wide aperture lenses are more prone to flare, even stopped down, so in some ways it makes sense. So less design compromises, even though use may be compromised in terms of narrow depth of field. I haven't seen the design, but I wouldn't mind betting it's similar to some of the classic designs of the 60's by the likes of Zeiss and Contax.